Impeller-less Water Jet propulsion

Discussion in 'Projects & Proposals' started by tom kane, Dec 1, 2010.

  1. tom kane
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    tom kane Senior Member

    Water jets have limitations in shallow water,sucking up sand,mud,weeds and blocking up. An Impeller-less water jet using the steam jet injector principle could be a usfull alternative. Air is also used in this method. Industries use steam injectors to evacuate large chambers to absolute vaccum. A virtual impeller consisting of a blade of compressed air spinning in place of metal impellers may be possible.
     

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  2. Yellowjacket
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    Yellowjacket Senior Member

    You could do that, but it won't be efficient at all.

    First of all there is the issue of mass transfer. An ejector works by transferring mass, and the air you are trying to use to move the water weighs a lot less than the water, so you need a huge volume of air to move some water. Since you won't get more than 80% efficiency out of the compressor, you have lost 20% even before you start.

    Air ejectors also use the heat of core flow to add energy to the exhaust stream. Using water would quench the exhaust flow unless there was enough hot air to boil all of the water, and that's not going to happen.

    What an ejector does is improve the propulsive efficiency of a small jet by decreasing the velocity of the jet and increasing the mass flow. I have worked with ejectors on missiles, but I don't thing that trying to use an air/water ejector is going to be an efficienct way of moving a boat.
     
  3. RonL
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    RonL Junior Member

    An observation I have made in a spa, but not tested, goes a little in line with Tom's idea. The jet of water by itself has a force that can be felt with one's hand, then opening the air valve brings in air that breaks into bubbles, adding what seems to be a greater increase in the force being ejected into the water of the spa.
    Using a water jet there will be less loss than compressing air, but with a diverging nozzle, energy of expanding air can possibly add some thermal energy to the jet discharge.

    Might not be much, but every little bit helps.

    Ron
     
  4. tom kane
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    tom kane Senior Member

    The discription impeller-less may be misleading as the air-water being pumped by the Water-cooled-lobe Pump into the water pump and jets spinning would constitute an impeller effect. I would be hopeful of achieving efficiency close to a diesel electric or a hydraulic system. A propulsion drive that does a job nothing else can do is better than none.

    Atmospheric pressure pushing down on the water would assist water flow into the water pump. Atmosphere replacing displaced air can travel close to the speed of sound giving a ram effect.
     
  5. rambat
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    rambat Member at large

    Impellorless

    Looks interesting They use this type of"pump" on mega yachts to keep bilges empty, low steadyflow no trash. But as a mud, sand and grass drive it would have to offer more than a MudBuddy:

    http://www.mudbuddy.com/

    Check out boating on lubricated, almost dry land!
     
  6. Yellowjacket
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    Yellowjacket Senior Member

    There are two pumps in a hot tub, one for water and onoe for air. When you turn on the air it increases the increases the velocity of the jet by shooting more volume into the system forces are higher, but it takes much more energy to compress air than it does water. For energy efficiency you want to pump water not air.
     
  7. RonL
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    RonL Junior Member

    I do have the air compressor, but this is air that is pulled in through a suction as water moves to the jet outlet. I suspect it is the same as a design found in a garden supply ferterlizer kit that attaches to a water hose.

    Whatever the design it seems to add a slight increase to the thrust, it might also add a few watts to the pump motor, but I would be surprised.

    It's the kind of small plus that would be overlooked or ignored in most systems.

    Ron
     
  8. CDK
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    CDK retired engineer

    Venturi-based pumps are a last resort solution because of the low efficiency. They are used in underwater construction and in the industry to pump aggressive liquids.
    I am not familiar with an application to excavate air; there are other ways to do that.

    A UK based company claimed they invented a steam jet propulsion device with the same efficiency as an outboard but showed only computer animations. When the deadline for a working prototype was due, they stated in a press release that the project was sold to an outboard manufacturer for further development.
    End of story.
     
  9. tom kane
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    tom kane Senior Member

    Images show a very crude model with just air tube, clamp it on your transom and away, swing from side to side to navigate. Design possibilities include low profile above water,better intake design possible. Cheap plastic molding of case and parts,no corossion rust..phewwww.
     

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  10. tom kane
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    tom kane Senior Member

    No suction is involved air is displaced and atmospheric pressure rushes in to fill all voids carrying all with it.
     
  11. baeckmo
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    baeckmo Hydrodynamics

    Well, CDK and Yellowjacket have covered the main issues here. Let me just add that thrust augmentation devices have been studied (and experimented with) in the marine environment for ages. For instance: in 1938 a "Schubvermehrer" ("thrust increaser") was patented by Mélot. The jet pump of the ejector configuration you propose, is just one example of known "Momentum exchanging devices". They suffer from high irreversible thermodynamic losses, like chock, turbulence and secondary flows.

    Say that the thrust from a propeller driven mechanically from an engine has the value 1, then the power for the water pump that drives your ejector would have to be ~5 times the engine power for the propeller, with a GOOD ejector design.

    If you have an "expendable" low-flow, high-velocity mass flow available from an onboard source, it is more efficient to let it do work through a turbine, which in its turn is powering a propeller. The so called "vane-tip turbine" is an example. This combination constitutes a "Work exchanging device", giving a maximum thrust augmentation if the primary and secondary fluids undergo an isentropic energy exchange, with the fluid mixture leaving the device in a pure axial flow, without internal velocity gradients.
     
  12. tom kane
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    tom kane Senior Member

    If Dyson dual cyclone vacuum cleaner took 15 years and 5,127 prototypes to get a marketable device I guess we will have to ignite the after-burners on this Paulse jet driven ejector water pump if we want an impeller-less water jet pump. There must have been millions of attempts to build something like this and very likely one already exists, that works well.
     

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    Last edited: Dec 5, 2010
  13. RonL
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    RonL Junior Member


    Tom,

    Not sure what I'm looking at :confused:

    Ron
     
  14. CDK
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    CDK retired engineer

    That is almost one prototype each day for 15 years.
    These are marketing fairy tales to impress a gullible public.
     
    Last edited: Dec 7, 2010

  15. tom kane
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    tom kane Senior Member

    I think that the moral of the story is that he did impress a lot of people and fixed the problem he was having with blocking up vacuum cleaners.He did not take much notice of people who said it won`t work or that it won`t be efficient and probably made a lot of money and friends..In othe words he was very persistent.

    Notice that the word suction is also mis-used here. A vacuum cleaner does not suck but displaces air and atmospheric pressure rushes in to replace the displaced air. Atmospheric pressurs pushes not sucks. Galileo v Torricelli discussions proved this with their experiments. It`s a fact.
     

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